The present invention relates to an improvement in a ground heater and more particularly to a portable apparatus used to defrost a small portion of frozen ground to a certain depth for ease in excavation.
In cold climates the ground can often be frozen to a depth of three feet or more. This frozen ground can be extremely difficult to excavate, as the moisture in the soil freezes producing a barrier similar to concrete. It is often necessary to place utility lines such as gas, water or electricity several feet below the surface of the earth. In order to service these lines it is necessary to excavate. The frozen ground can make this excavation similar to digging through cement. Heavy equipment is available to perform this task, but such can be extremely dangerous near gas or other lines making it necessary to dig manually. Several devices are known which may be used to thaw a small section of ground prior to excavation. These devices defrost and thereby soften the ground aiding so that the manual excavation of dirt may be possible.
U.S. Pat. No. 5,441,038 issued to Ohmann discloses a ground thaw device using a chamber with sidewalls and a roof made of an insulating material. The chamber has a port that is substantially airtight to the outside and made to receive a burner. As the port is substantially closed, large amounts of heat can build in this area creating problems. The device may also be fitted with a fan which may be used to dissipate this heat, adding to the complexity of this device.
U.S. Pat. No. 5,033,452 issued to Carriere also discloses a thawing device with a thermally insulated housing. This device uses a burner mounted inside a fire tube. The housing in this device uses a pitched roof with a steam vent at its apex. This vent allows for the escape of steam and thus, heat. It has been found that steam may greatly aid in thawing the ground as it penetrates and softens the earth.
U.S. Pat. No. 4,349,010 issued to Bentham generally discloses a frost removal system which uses a series of heating pipes. These pipes are placed on the ground for thawing.
As can be seen from this discussion it would be desirable to have a highly portable device for thawing a portion of earth and order to allow for its excavation. This device should be light enough to allow a single person without assistance to transport setup and use. This device should be able to run for extended periods of time on small amounts of gas and be safe to operate.
It is the primary objective of the present invention to provide a method by which a defined area of ground can be thawed to a depth of three feet during the cold winter months which will allow individuals to evacuate soil from previously hard frozen earth to gain access to buried cables, water lines, gas lines, or other similar utilities that are commonly placed below the surface of the earth. It should be stated at this point that this device should be useful for defrosting a small portion of ground any time as necessary to aid in its excavation. Further the user may incorporate more than one device at a time if necessary to thaw a larger area.
It is an additional objective of the present invention to provide such a method of thawing frozen earth that does not require the use of a great deal of heating fuel and therefore operates in an efficient manner.
It is a further objective of the present invention to provide such a method of thawing frozen earth that is extremely portable and is designed and constructed in a manner that allows a single person to easily and effectively to both operate the device and transport it from place to place.
These objectives are accomplished by the use of a shallow rectangularly shaped box-like apparatus (or thaw body) that is open-ended on the side that would normally form the floor of the thaw body. This open-ended box is constructed with a high degree of insulating value and is designed to trap heat against the surface of frozen ground. The insulating qualities of the thaw body are accomplished by building the walls of the box in a double-walled fashion. This means that all the walls will have both an inner and outer wall which leaves an open space between them. This space may then filled with a commonly available insulation material such as fiberglass or foam insulation. This method of construction ensures that the interior of the thaw body retains the maximum amount of any heat that is directed into it and enables the present invention to operate in the most efficient manner possible while being employed to thaw frozen ground during the winter months.
The heating requirements of the present invention are supplied by the use of an externally mounted radiant propane heater that is commonly available in the marketplace today. One such heater is sold under the name MR. HEATER or commonly referred to as sunflower heads. This attachment is built into one of the short vertical walls on the end of the thaw body by placing the burner element of the radiant heater in the most outward opening of the vented heat transfer tube. The vented heat transfer tube is a cylindrical opening that passes from the outside of the thaw body to the inner body cavity and which is made up of an inner and outer tube. The outer tube is a cylindrical opening of the thaw body wall while the inner tube is a separate and relatively short section of a tube that is somewhat smaller in its outside diameter than the inside diameter of the outer tube. Additionally, the inner tube is permanently attached to the most outer end of the outer tube and extends outward therefrom in a manner so that it extends beyond the outer wall of the thaw body. The attachment of the inner tube to the outer tube is also made in such a manner so that its orientation is offset with respect to the position of the outer tube. This offset of the inner tube is critical to the spirit of the invention as it leaves a gap between the inner and outer tubes that allows for the free flow of air to the radiant heater. This free flow of air to the heater enhances the efficiency of the radiant heater and therefore increases the operational effectiveness of the invention.
Once the radiant heat is channeled into the thaw body of the present invention, it encounters the reflector shield that is attached to the upper inside surface of the thaw cavity. The reflector shield is a reflective plate attached to the thaw cavity by the use of a plurality of bolts and wing-nuts. The reflector shield serves the purpose of directing the heat generated by the radiant heater in a downward manner which forces it to encounter the earth. Further, all inner surfaces of the thaw body may be coated with a reflective surface to reflect the radiant heat toward the ground. Thus, this design transfers the heat generated by the radiant heater into the internal cavity of the thaw body and then directs it in a downward manner where it contacts and effectively thaws frozen ground.
For a better understanding of the present invention, reference should be made to the drawings and the description in which there are illustrated and described preferred embodiments of the present invention.